Beginning of Essay
? The human eye does alot more than allowing you to see. It is very complex and has many parts and features which can have defects. However, to understand defects you must first know how the eye works. First light passes through the cornea, which is the transpa ....

Middle of Essay
.... reverse and upside-down. Finally light- sensitive cells in the retina transmit the image via the optic nerve to the brain by electrical signals. Then the brain flips the image so it looks right- side-up to you. You can find a diagram of the above on page 3. The most common visual defects are nearsightedness and farsightedness. In nearsightedness, also known as myopia, the eye is longer than usual. This is corrected by using a concave lens to spread the light rays just enough to increase the eye's focal length. Hyperopia, also known as farsightedness, is caused by a shorter than usual eye. A convex lens increases light bending and returns the p ....